Modern internal combustion engines often utilize aftertreatment systems to achieve emissions regulatory targets. Some aftertreatment systems include an oxides of nitrogen (NOx) reduction device, such as a catalyst for a selective catalytic reduction (SCR) system. Aftertreatment system control systems can be enhanced by detection of a failed or off-nominal NOx sensor. In some cases such detection is required by regulation. Detection of failed sensors can indicate that need to use an alternate NOx determination method and/or to set a failure indicator.
NOx sensors that are commercially viable for field use with an internal combustion engine have an interference with ammonia (NH3), erroneously detecting a significant percentage (80% or higher) of NH3 as NOx. Further, reactions within the NOx reduction device cause a difference to occur from the NOx-in to the NOx-out that is not attributable to the sensors. Therefore, merely comparing sensor signals during engine operations will not generally allow a determination of a failed or off-nominal sensor. Furthermore, suspending the dosing of NH3 or other reductant during a diagnostic of the NOx sensor results in the possibility of increased NOx emissions and increased doser tip temperatures. Therefore, further technological developments are desirable in this area.